Australia are waiting anxiously for results of a scan on captain James Horwill's shoulder.

The Wallabies lock, who replaced Rocky Elsom as skipper prior to the Rugby World Cup, regularly ices the shoulder after games. But it was decided on Sunday night that he should have an MRI scan to rule out fears of a more serious injury.

Wallabies official insisted it was a precautionary measure but the injury is clearly an increasing concern for Australia, who are already without flanker David Pocock and winger Digby Ioane with back and thumb injuries.

Both Pocock and Ioane missed the crucial 15-6 defeat to Ireland in Pool C on Saturday. And centre Antony Faingaa is now suffering from the same illness that kept hooker Stephen Moore out of the match with Ireland.

Faingaa remained in Auckland while his team-mates traveled to Wellington but should join them on Monday ahead of the Wallabies clash with the USA on Friday.